So you have a single mobile device connecting via wg, correct? Not a second network?

If so the only configuration you should need on the router are firewall rules to allow forwarding from wg to lan. I am guessing that’s what the second step in the GL-iNet help accomplishes. That’s what I would recommend trying.

If I was doing this on “normal” OpenWRT I would create a firewall zone wg, and allow traffic to/from it and lan.

On the client device you should be good to go without changes if AllowedIPs is set to 0.0.0.0/, ::/0 (sending all traffic through wg).

That rule is supposed to be set on the “server” at the other end of the wg connection, using its own wg address as gateway. Not on the router for the lan you’re trying to access. That seems like a pretty easy mistake to make given that documentation.

You could try a short reset of just the network configuration. Hold reset for like 5 seconds. Might need to do a full reset (10+ seconds) if that doesn’t get you back in.